A plasma display panel (hereinafter, called PDP) which meets the needs for higher definition and a larger screen is often used in 100-inch or larger televisions. In recent years, there is an ongoing trend to use the PDP in high-definition televisions in which scan lines are at least doubled as compared with a conventional NTSC televisions. Another recent trend is lead-free PDPs, which were launched in the market to contribute to an environmental protection.
The basic structural elements of the PDP are a front panel and a back panel. The front panel has a glass substrate made of sodium borosilicate glass by the float method. On one of the main surfaces of the glass substrate are formed display electrodes consisting of stripe-like transparent electrodes and bus electrodes. The display electrodes are covered with a dielectric layer functioning as a capacitor, and a protective layer made of magnesium oxide (MgO) is formed on the dielectric layer. In the back panel having a glass substrate, stripe-like address electrodes are formed on one of main surfaces of the glass substrate. The address electrodes are covered with a ground dielectric layer, and barrier ribs are formed on the ground dielectric layer. Phosphor layers, which respectively emit red, green, and blue lights, are formed between the barrier ribs.
The front panel and the back panel are air-tightly sealed with their electrode-formed surfaces facing each other. Ne—Xe discharge gas is enclosed at a pressure between 55 kPa and 80 kPa in a discharge space which is divided by the barrier ribs. The PDP generates an electric discharge by selectively applying a video signal voltage to the display electrodes, and ultraviolet generated by the discharge excites the phosphor layers to make them emit the red, green, and blue lights so that a color image is displayed.
Silver electrodes are used to ensure conductivity as the bus electrodes constituting the display electrodes, and low-melting glass containing lead oxide as its principal ingredient is used in the dielectric layer. Faced with the environmental consciousness escalating in recent years, lead-free dielectric layers were disclosed (for example, see the Patent Documents 1, 2, 3, and 4).
According to the conventional technology, the front panel was provided with, generally called transparent electrodes, which transmit visible light to ensure an expected numerical aperture. However, different approaches are currently underway to reliably obtain conductivity by providing metal electrodes alone in the display electrodes while omitting the transparent electrodes for cost reduction.
In the conventional structure, two display electrodes are formed in one scan line, and one transparent electrode and one metal electrode are formed in one display electrode. The omission of the transparent electrodes, however, inevitably increases number of metal electrodes to be provided in one display electrode in a ladder-like structure to ensure conductivity. Silver (Ag) included in the metal electrode has a large coefficient of expansion. Therefore, a stress exerted in the direction of compression is applied to the glass substrate after the dielectric layer is formed. Thus, a residual stress generated in the glass substrate has the direction of compression.
As a larger number of metal electrodes are provided, the residual stress of the glass substrate further increases in the direction of compression in proportion to a total area of the metal electrodes. In the case where the residual stress of the glass substrate after the dielectric layer is formed in the direction of compression, a residual stress of the dielectric layer on the film-surface side, on the other hand, is exerted in the direction of tension. With the respective stresses being thus reversely generated, the front panel may collide with the back panel when they are disposed facing each other to be sealed. The collision may generate fine cracks, accelerating substrate breakage. Another problem is a voltage load imposed on the fine cracks generated in the dielectric layer when an image is displayed, resulting in insulation failure in any portions where the cracks are generated. In addition, in a lead-free dielectric layer, this phenomenon remarkably occurs.
A main object of the present invention is to provide a PDP capable of reliably acquiring a remarkable luminance level and a high reliability during a high-definition image display and meeting the needs for environmental protection.